A conventional internal combustion engine uses a crankshaft to couple the reciprocating motion of a piston with the rotating motion of a drive shaft. In such devices the piston is coupled to a crank pin via a connecting rod, and the crank pin is carried on a crank arm in a circular orbit about the central axis of the crankshaft. The crankshaft in turn is coupled to the drive shaft. In many engines and motorized vehicles, multiple pistons are coupled to the same crankshaft.
Internal combustion engines typically produce power by combusting a charge of fuel such as gasoline or diesel inside the cylinder. Theoretically, the efficiency of an engine can be maximized by instantaneously combusting the entire charge at top dead center (TDC), i.e, when the volume of space defined by the piston and the cylinder is at a minimum. In practice, however, this is difficult or impossible to accomplish. Modern engines compensate for the time it takes to combust the charge by beginning combustion before top dead center (BTDC), and in some cases well before top dead center. In modern gasoline engines the charge may be ignited with a spark plug anywhere from 5 degrees to more than 60 degrees BTDC, with a greater advance being required to compensate for higher engine speed. This is commonly referred to as spark advance. Diesel engines utilize a corresponding combustion advance without a spark, but in diesel engines the charge detonates rather than burns, and therefore less advance is required. The smaller advance in diesel engines is generally regarded as a significant factor in the greater efficiency of diesel engines relative to gasoline engines.
One of the drawbacks to beginning combustion before top dead center is that work generally must be expended compressing the combusting gas--the greater the advance, the more energy is expended. The amount of energy expended in this manner may be quite significant, and many improvements have been directed at reducing the time it takes for combustion to occur. For example, efficiency has been increased somewhat by more accurately controlling the fuel mixture through the use of fuel injection; by swirling and atomizing the injected fuel to improve its mixing with air inside the cylinder; and by using side chambers in which an especially rich fuel mixture can be quickly ignited. Despite these improvements combustion of 90% of the charge may still require at least 30-50 degrees of crank angle at about 1200 RPM, and even more crank angle at higher speeds. Moreover, even with a relatively large combustion advance, a significant portion of the charge may still be combusted after top dead center, which further reduces efficiency.
Thus, there is a further need to minimize the negative effects of combustion duration. This is especially important with respect to motorized vehicles including, for example, automobiles, planes and boats, in which inefficiency is associated with considerable monetary and pollution costs.